Fatty acid-induced modulation of ouabain responsiveness of rat Na,K-ATPaseisoforms

Membrane phospholipids represent a potential influence on the enzymatic pro perties of the Na,K-ATPase. Little is known concerning the effects of the f atty acid environment surrounding the enzyme on the kinetic properties of t he Na,K-ATPase. We used the most obvious difference among the cr. isoforms of rat, their affinities for digitalis glycosides, to examine the relations hip between the lipid environment and the Na,K-ATPase. Specific membrane en vironments that differ in their fatty acid composition were produced by dru g-induced diabetes, as well as variations in diet. The alpha 1 isoforms in various tissues were then characterized by their resistance to ouabain in N a,K-ATPase-enriched membrane microsomal fractions. The Na,K-ATPase activity in nerves and hearts were altered by diabetes and partially restored in ne rves after a fish oil diet. Evaluation of enzyme kinetics (dose-response cu rves for ouabain) in membrane preparations allowed us to correlate the ouab ain affinity of alpha 1 isoform with fatty acid composition. The affinity o f the alpha 1 isoform for ouabain was significantly increased with accretio ns in the total amount of fatty acids of the n-6 series (P < 0.0001). Our o bservations provide a partial explanation for the observed difference in is oform properties among tissues. Moreover, these results underline the inter action between membrane fatty acids and the glycoside binding site of the N a,K-ATPase alpha 1 subunit.